Re: Why does the amount of catalase activity vary in different tissues?

Elle,
      The activity of most enzymes, not just catalase, differs from one 
type of tissue to the next.  This is not due to any difference in the 
enzyme itself, but to the fact that different tissues have different 
amounts of various enzymes.  Different organs in our body share many of the 
same enzymes, but in very different quantities.  
     Different species (such as the apple and potato that you mentioned) 
frequently share slightly different forms of enzymes that carry out the 
same catalytic reaction.  While these isozymes, as they are called, can 
differ somewhat in their activity, the biggest difference between the 
enzymatic activity of a tissue sample from one plant species compared to 
another is most likely due to differences in the amounts of the enzymes 
that are present.  Similarly, if you examined catalase activity in the 
fruit compared to the leaves of a particular plant, you would be very 
likely to find different levels of activity.